Thin-layer drying of parchment Arabica coffee by controlling temperature and relative humidity

This paper presents thin-layer drying of parchment coffee (Coffea arabica). Thin-layer drying of parchment coffee was conducted under controlled temperatures (50°C, 60°C, and 70°C) and relative humidities (10%-30%). The temperature of the drying air was important for drying at a high temperature, which results in the rapid removal of moisture and reduced time for drying. Nine thin-layer drying models (Newton, Page, Henderson and Pabis, logarithmic, two-term, modified Henderson and Pabis, two-term exponential, approximation diffusion, and modified-Midilli) were fitted to the experimental data for parchment coffee. The drying parameters of parchment coffee were related to temperature and relative humidity. The best model was the modified-Midilli model, which can be used to design the optimal dryer. The effective moisture diffusivity of parchment coffee drying was determined by minimizing the sum of squares of the deviations between the experimental data for the moisture content and the predicted values of thin-layer drying. The effective moisture diffusivity as a function of the temperature at each relative humidity was expressed by the Arrhenius-type equation.